Salmon salad with potatoes and tomatoes

Boil the potatoes in shell. Peel, cut into cubes and place in a bowl.
Cut the salmon into cubes and add to bowl over the potatoes.
Wash well and chop onion.
Dice tomatoes and add with onion over the other ingredients.
Season with salt and pepper to taste, then add sour cream and mustard.
Serve chilled.